Machines of the type used for compacting ballast of a ballast bed of a railroad track are known in the art. Generally, these machines comprise a machine frame, undercarriages supporting the machine frame on the track rails for movement in an operating direction, and a track stabilization unit mounted on the machine frame. The track stabilization often includes a chassis, guide roller means firmly holding the chassis in engagement with the track rails and guiding the chassis along the track upon movement of the machine frame in the operating direction, vibrator means for imparting essentially horizontal vibrations to the track, and power drive means connecting the chassis to the machine frame and arranged to impart essentially vertical load forces to the chassis. The machine may have control means for operating the track stabilization units and other workheads which may be provided on the machine.
A machine of this general type has been disclosed, for example, in U.S. Pat. No. 3,926,123. This machine has a frame supported on two undercarriages and having a frame portion overhanging the front undercarriage. The tamping unit is mounted on the overhanging frame portion and the track stabilization unit is mounted on the machine frame between the two undercarriages. With this machine, the track is brought to the desired level, is fixed at this level by tamping the ballast under the track-supporting ties, and the position of the leveled track is then stabilized. Another such machine is disclosed in U.S. Pat. No. 4,046,078. This machine has a mobile machine frame supporting a track stabilization unit between two undercarriages. During the dynamic track stabilization effected with these prior art machines, the previously tamped ballast is so fluidized as to become denser, thus reducing the volume of the ballast bed and causing the track to sink to a lower level. This anticipates the kind of ballast settling occurring normally under train traffic subsequent to track tamping operations and enhances the resistance of the tamped ties to transverse movement relative to the ballast bed. Since the track stabilization unit chassis is downwardly pressed while being vibrated horizontally in a direction transverse to the track, it causes the firmly gripped track to be embedded in the fluidized ballast against lateral movement of the ties while the ballast is further densified. In this manner, the tamped ballast is further compacted under the ties and at their sides, which reduces the ballast volume and lowers the level of the track supported thereon.
In order to provide maximum horizontal vibration force to the track stabilizer, various apparatuses and methods have been introduced to maximize the horizontal vibration, while minimizing or neutralizing the vertical forces. One such apparatus is the Plasser Dynamic Track Stabilizer (DTS). The Plasser DTS has two (2) vibrating workheads connected in series by drive shafts to synchronize the vibration. In each unit there are two (2) equal rotating weights, one above the other, geared to rotate in opposite directions. In this configuration, the weights and shafts are designed such that when one weight is moving upward, the other is moving downward. This neutralizes the vertical force associated with the rotating weights. When the weights are towards the left or right, they become additive and create a left to right oscillating force. The magnitude of this force varies with the speed of rotation of the weights, reaching a maximum of 19.5 tons at 33 Hz. Weight is transferred vertically from the machine to the vibrating workheads by hydraulic cylinders, thereby allowing the control system of the machine to increase or decrease the settlement of each rail. This can be up to 50,000 pounds per side.
Another apparatus is the Harsco Rail/MTH DTS. This apparatus or unit utilizes a similar concept of rotating weights to create the left to right vibration which is imparted into the rails. The weights are located on a single carriage with the shafts being vertical. When the weights are moving apart or together in the longitudinal direction of the rails, the forces cancel. When they are moving towards the rails, either left or right, the force is additive. The maximum lateral force is 50 tons at 45 Hz. Weight is transferred vertically from the machine to the vibrating workhead by hydraulic cylinders in a similar fashion to the Plasser unit.
While these machines and apparatuses have proven effective, in order to provide the required reaction for the vertical or downward force applied to the workhead, it is necessary to add a significant amount of weight to the machine. This results in machines which require a significant amount of steel to provide the required weight. As a result, it becomes necessary to have larger axles, a more powerful drive train, and greater braking efforts. All of these things increase the cost of the machine.
It would, therefore, be advantageous to have a machine in which the vertical reaction capability could be provided without the need for the increased weight of the machine, thereby reducing the size and cost of the machine while still providing the necessary vibration and downward force required to properly stabilize the ballast and the track.